Modeling and Mitigation of the Effect of Free Space Optical Attenuation during Fog at UHF Band

Free space optical communication (FSOC) is a new communication technology that uses LASER beam to transmit high quality signals through the atmosphere with more data security. In this work, field measurement of signal strengths at five unlicensed ultra-high frequencies (900, 1200, 1400, 1600 and 1800 MHz) at various visibility during fog has been carried out. The measurement was carried out using a developed optical transmitter and receiver capable of transmitting and receiving optical signal strength within UHF band. The experimental data analyzed based on the best fit curve shows that, generally, the optical signal attenuation in fog decreases with increasing visibility. The lower frequency (900 MHz) suffered less attenuation (11.90 dBm) while the higher frequency (1800 MHz) suffered more attenuation (19.19 dBm). Hence, applying frequency diversity by telecommunication industry will mitigate the effects of FSO attenuation during fog. Furthermore, the results obtained were compared with ITU-R frequency dependent attenuation model and the root mean square error obtained was 16.81, a new model for predicting optical signal attenuation during fog weather at UHF band was developed. The value of R2 obtained was 0.9538 which indicates that the model developed is considered to better fit the measured data. The correlation coefficient, r, between the optical signal attenuation and the frequencies is 0.9797 which indicates a rise of 9.98 dBm in signal attenuation to a rise in frequency by 10%.